CEM 351 Quiz 3: Questions and Answers on Organic Chemistry Reactions - Prof. James Jackson, Quizzes of Organic Chemistry

Download CEM 351 Quiz 3: Questions and Answers on Organic Chemistry Reactions - Prof. James Jackson and more Quizzes Organic Chemistry in PDF only on Docsity! Name: Student #: Section #: TA: CEM 351 Quiz 3 Friday, November 5, 2004 1. (12 pts) Quick answers from Jones, Chapters 8-10.2: (a) (2 pts) Which of the following alcohols could you make via hydroboration/oxidation? OH HO (b) (2 pts) Circle the energy diagram for the exothermic reaction: E Reaction Coordinate Reaction Coordinate (c) (2 pts) Circle the more stable carbocation: (d) (3 pts) Which one of the three dibromocyclohexanes below would expect from reaction of Br2 with cyclohexene: Br Br Br Br Br Br A B C (e) (1 pt) Which one of the compounds as shown in (d) is chiral? A B (f) (2 pts) In the equilibrium H2 + I2 <==> 2 HI, which side would be favored? Use these bond dissociation energies (BDEs) to determine whether the reaction is exo- or endothermic: H-H 104.2 kcal/mol; I-I 36.1 kcal/mol; H-I 71.3 kcal/mol. Now circle your expectation for the preferred side. Right Left Overall energy change = 104.2 + 36.1 – 2 x 71.3 = -2.3 kcal/mol i.e. exothermic 2. (8 pts) Reaction of cis-2-butene with hydrogen bromide gives racemic 2-bromobutane. Br Br +HBr + (a) (4 pts) Show carefully (by writing a mechanism) the origin of the two enantiomers of 2- bromobutane. Br Br + Br H Br– bottom attack on sp2 cation top attack (from bottom attack) (from top attack) (b) (4 pts) In addition to the 2-bromobutane, small amounts of two alkenes isomeric with the starting material can be isolated. What are these two alkenes (draw and name them) and how (mechanism?) are they formed? (Hint: don’t forget all these reactions are reversible.) 1-butene from (a) E-2-butene from (b)free rotation here lose a proton here (a) or here (b)